by M. Marvan
Arch. Math. (Brno) 21 (1985) 51–64.
In this paper coalgebras mean algebras over the category Setop. We study them under various approaches known in categorical algebra. Obtained are constructions of cofree coalgebras in quasicovarieties (HS-closed classes of coalgebras) as well as theorems of Birkhoff type characterizing covarieties (HSS-closed classes of coalgebras).
Errata: On page 55, line 15, remove underlining from the first two occurrences of "ker". Underline the fourth occurrence of "ker".